Process for continuous-tone printing plates



March 28, 31944. s ss s 2,345,447

PROCESS I OR CONTINUOUS-TONE PRINTING PLATE Filed Nov. 11, 1942 1119.1. (g\\\\ \\\\\\\\\}\\\\\\\\\\\\\K ALCOHOL AND CLAY 2 wars? REPfLLf/VT LAYER WATER REPELLENT L AYE? .1219 a. POLYVI/VYL ALCOHOL AND 1 CALCIUM CARBON/17'! 1 V 'uvwuxuww'KKRK'WWR" POI-YWNYL ALCOHOL AND CLAY f- 7 WATER REPELLE/VT LAYER I X 24 1/ 77 -WATER REPELLENT LAYER 5 POLYV/NYL mean/o1. AND 1 CALCIUM CARBON/TE a POLYV/NYL ALC H L AND CLAY Z WATER REPELLE/V LAYf/P PAPER 2 WA TE REPEL L E N T L A YER AL BUM/N AMMON/UM 01c HROMA TE 9- POLYV/NYL ALCOHOL AND CALCIUM CARBONATE VINAL ALCOHOL AND CLAY ER REPELLENT LAYER PA Pm 1 Tm REPEL 1. EN T 1. A YER Y PRINTING POI? TIC/V5 LBUMIN AMMO/V/UM DICHROMATE POLYVINVL ALCOHOL AND CALCIUM CARBON/TE YVINYL ALCOHOL AND CI AY TER REPELL EN T L A YER PA PER TER REPELLE/YT LAYER 6 I mm fl%wne Patented Mar. 28, 1944 PROCESS FOR CONTINUOUS-TONE PRINTING PLATES Ellis Bassist, Brookline, Mass.,

assignor to William Craig Toland, Brookline, Mass., as

trustee Application November 11, 1942, Serial No. 465,257

8 Claims.

This invention relates to printing and more especially to planographic printing plates and methods of preparing planographic plates.

An object of the invention is to improve planographic printing plates and methods of making planographic printing plates, and to devise a method of making a planographic plate of the continuous-tone type, with a viewto providing a substitute for reticulated colloids, such as gelatin, and thereby overcoming difliculties now encountered in connection with the use of such materials. Another object of the invention is to devise an improved sheet material for use in making a continuous-tone printing plate. Another,

object of the invention is to provide a simple, cheap and efficient printing plate of the continuous-tone type.

In the accompanying drawing:

Figure 1 is a view in cross section illustrating a base element employed in making the printing plate of the invention;

' Fig. 2 is a view in cross section illustrating a printing plate material of the invention;

Fig. 3 is a cross sectional view illustrating a step in a method ofconverting the printing material illustrated in Fig. 2 into a planographic printing plate;

Fig. 4 is another cross sectional view illustrating a further step in the method referred to; and

Fig. 5 is a cross sectional View illustrating still another step in the method noted.-

The method of the invention generally includes providing on a water-receptive planographic base element a thin coating made up of a binder and a filler, and then treating the coating to cause it to become converted into a finely reticulated state, such that it is useful in the preparation of a continuous-tone printing plate.-

Referring more in detail to the invention, Figure 1 illustrates one suitable base element which I may employ in making the plate of the invention. This base element is of the type described and claimed in my copendingapplications, Ser. No. 429,672 filed February 5, 1942, and

Ser. No. 414,254, filed August 9, 1941. The base includes a specially sized paper element I, which is treated at either side with a water-repellent material 2, and which is further provided on at least one side thereof with an outer coating 3 made up of a water-receptive printing body. The

water-receptive printing body 3 preferably consists of water-swellable cold-water-insoluble polyvinyl alcohol and clay.

The water-repellent material 2 keeps the..paper I from absorbing water and prevents stretching and shrinking when the plate is subjected to water as employed in the development and use of a planographic printing plate. The polyvinyl alcohol and clay coating constitutes a water-receptive lithographic surface and is attached to one of the water-repellent layers sufliciently strongly to withstand separation when subjected to the stresses encountered in lithographic printing operations.

In carrying out the method of the invention the planographic base element noted is .provided with a surface coating 4, consisting of a binder and a filler, preferred embodiments of which are water-swellable, cold-water-insoluble polyvinyl alcohol and calcium carbonate. Other fillers are Calflx," Warrenite," blanc fixe, and others. The coating 4 is spread thinly over the surface of'the coating 3, as is diagrammatically illustrated in Fig. 2 of the drawing.

In accordance with a further step in the method of the invention, the coating 4, after being dried at room temperature, is subjected to heat (-200 F.). The result of the heating treatment is to cause the coating 4 to crawl upon it self and become ,cracked, thereby forming a substantially uniformly reticulated surface 5, as has been diagrammatically illustrated in Fig. 3 of the drawing.

Over the reticulated surface 5 is applied a lightsensitive coating 6, as for example one including albumin and ammonium dichromate. This coat ing 6 is allowed to dry and is then exposed to actinic light passed through a photographic negative without the use of a screen. Thereafter the exposed portions of the albumin are rendered grease-receptive to form ink printing portions 1, while the unexposed .portions are washed away in accordance with conventional developing procedures, such as are resorted to in the albumin process. Figures 4 and 5 are intended to be illustrative of these operations. Other means of applying a greasy image, as by drawing with a greasy crayon or other ways, may be resorted'to.

An important feature of the invention consists in the use of polyvinyl alcohol and calcium carbonate coating and the step of heating to reticulate this coating to form a suitably grained surface. The reticulated surface obtained by heatscreen eflects are employed. The reticulation of the gelatin commonly takes the place of the screen, allowing satisfactory reproduction of light and dark areas to take place. The reticulated polyvinyl alcohol and calcium carbonate constitute a similar type of surface to that constituted by gelatin which has been allowed to become reticulated, with the advantage that the polyvinyl alcohol and calcium carbonate is of a more uniform and durable character. The tiny cracks and fissures resulting from the polyvinyl alcohol and calcium carbonate contracting upon itself provides a grain which is highly adapted to insuring faithful reproduction of subject matter obtained from ordinary photographic negatives.

A modification of the method of the invention consists in applying on a planographic base of the character described, a coating of calcium carbonate in the manner already described. The coating is heated to form minute reticulations and greasy printing portions are formed on the reticulated calcium carbonate surface by some suitable means, as by the albumin process already described, or by drawing or writing upon the surface of the calcium carbonate with a greasy ink Or pencil. Thereafter the surface of the plate containing tiny dots of the greasy inking material making up the printing portions is treated with an acid as for example a mixture of weak nitric acid and gum arabic, or other etching acids commonly resorted to. This acid attacks the calcium carbonate particles to a limited extent, as is evidenced by a slight agitation or etching action, and in so doing tends to decrease the size of those particles which are covered with greasy printing material, thus increasing the size of the spaces occurring in and around the particles. resulting from the reticulation already described. By this means, the tiny ink dots are thus rendered sharper to an extent which may be controlled as desired, and there is afforded a continuous-tone printing effect of useful and desirable character.

It should be understood that the sharpened printing image effect thus obtained results from practicing the several steps of using calcium car bonate, supported on a water-receptive base, causing the calcium carbonate to become finely reticulated, and then etching away with acid portions of the calcium carbonate to accentuate the reticulation and reduce the spacing of the ink dots making up the continuous-tone printing image.

It should be observed that the outer coating of polyvinyl alcohol and calcium carbonate, upon exposure to heat, functions in a very different mannerfrom that which occurs with respect to the underlying polyvinyl alcohol and clay. The reason why reticulation occurs with respect to the polyvinyl alcohol and calcium carbonate and does not with respect to the polyvinyl alcohol and clay is not fully understood. It is believed that the calcium carbonate tends to swell to a very minute degree, and that when thereafter sub-' Similarly, other fillers'than calcium carbonate may further be utilized in conjunction with a grained metal plate or other types of water-receptive planographic bases.

It will be observed that I have provided a simple, cheap and efiicient planographic printing plate element, consisting of a water-receptive base of some one of the types noted, having superimposed thereon a. thin layer of a water-receptive body which upon exposure to heat is adapted to become suitably reticulated to constitute a continuous-tone printing plate. It is intended that this element may be made, sold and shipped as an article of manufacture. It is also believed that the step of utilizing a coating of this nature and subjecting it to heat while supported upon a second coating, is desirable and an improved method of making continuous-tone printing plates.

While I have shown a preferred embodiment of my invention, it should be understood that various changes and modifications may be resorted to, in keeping with the spirit of the invention as defined by the appended claims.

I claim:

1. That improvement in methods of making planographic printing plates which comprises providing a water-receptive base element which.

includes a coating of polyvinyl alcohol and clay, applying over the coating of polyvinyl alcohol and clay a second coating of polyvinyl alcohol and calcium carbonate, drying the plate, heating to a point at which the calcium carbonate and polyvinyl alcohol become reticulated, then coating over the reticulated surface of polyvinyl alcohol and calcium carbonate a suspension of albumin and ammonium dichromate, exposing to actinic light and developing.

2. That improvement in methods of making planographic printing plates which comprises providing a water-receptive base element which includes a coating of polyvinyl alcohol and clay, applying over the coating of polyvinyl alcohol and clay .a second coating of polyvinyl alcohol and a finely divided material, said second coating being adapted upon'exposure to heat to contract upon itself and break into a multiplicity of cracks, then a plying over the second coating a suspension of albumin and ammonium dichromate, exposing to actinic light and developing.

3. That improvement in methods of making planographic printing plates which comprises providing a water-receptive base element which includes a coating of polyvinyl alcohol and clay, applying over the coating of polyvinyl alcohol and clay a second coating of polyvinyl alcohol and calcium carbonate, drying the plate, heating the plate to a point at which the second coating of calcium carbonate and polyvinyl alcohol becomes reticulated, forming greasy printing images on the surface of the reticulated second coating, and etching the plate.

4. That improvement in methods of making planographic printing plates which comprises providing a water-receptive planographic printing plate base element, applying over the waterreceptive base element acoating of polyvinyl alcohol and calcium carbonate, drying the coating,

heating to a point at which it becomes reticu- Y lated, forming greasy printing images on the coating, and then treating with an acid to attack the calcium carbonate of the coating.

5. That improvement in methods of making planographic printing plates which comprises providing a water-receptive planographic printing plate base element, applying over the base element a, coating of calcium carbonate and a binder, drying the plate, heating the calcium carbonate coating to a point at which it becomes reticulated, and then etching with an acid adapted to attack the calcium carbonate.

6. That improvement in methods of making planographic printing plates which comprises providing a water-receptive planographic printing plate base element which includes a coating of polyvinyl alcohol and a finely dividedn inert material, applying over the coating of polyvinyl alcohol and inert material a second coating of polyvinyl alcohol and calcium carbonate, drying, and heating the calcium carbonate coating to a point at which it becomes reticulated, forming greasy printing images on the reticulated calcium carbonate coating, and then treating the printing image with an acid which is adapted to at-, tack the calcium carbonate.

I. That improvement in methods of making planographic printing plates which comprises an providing a water-receptive planographic printing plate base element which includes a coating of polyvinyl alcohol and clay, a second coating of polyvinyl alcohol and a finely divided material,

heating said second coating to cause it to contract upon itself and become reticulated, then forming a greasy printing image on the reticulated second coating.

8. That improvement in methods of making 0 printing plates which comprises providing a water-receptive planographic printing plate base element which includes a coating of polyvinyl alcohol and clay, applying over the water-receptive base element a coating of a binder and a 15 finely divided material, heating said coating to cause it to contract upon itself and become reticulated, then forming a greasy printing image over the reticulated coating.

ELLIS BASSIST. 

